During surgical operations, patients often lose a significant amount of blood. To avoid serious complications, this blood volume is often replaced. In particular, whole blood or a blood component is transfused into the patient. To maintain adequate supplies of blood and blood components, many hospitals and blood banks rely on donors who are typically un-related to the transfusion recipients. Despite rigorous testing protocols, there remains some risk of transmitting blood-borne diseases during transfusions. Thus, it is desirable to limit or even avoid, if possible, transfusions of donated blood. One way of reducing the reliance on donated blood is to collect the patient's own blood that is shed during surgery. This blood may then be processed by a blood recovery system and re-infused into the patient. By salvaging a patient's own blood, one can limit the amount of donated blood that the patient must receive, thereby reducing the risk of exposure to blood-borne diseases.
U.S. Pat. No. 5,634,893, for example, is directed to an autotransfusion system that recovers shed blood. FIG. 1 is a block diagram of the '893 system 10. The system 10 includes a compound reservoir 12 having upper 16 and lower 14 chambers that are interconnected by a drain valve 18. A suction tube 22 connects a wound or surgical site to the upper chamber 16 which is also connected to a vacuum source 32. A selector valve 38 selectively couples the lower chamber 14 to the vacuum source 32 or to atmospheric pressure. Normally, the valve 38 is positioned so that the vacuum is applied equally to both chambers 14, 16. That is, the absolute pressure in both chambers 14, 16 is the same. Accordingly, blood from the surgical site is drawn through suction tube 22 and into the upper chamber 16. The blood first flows through a particle filter 20 located in the upper chamber 16 to remove debris, such as blood clots, bone chips, etc. The filtered blood then collects in the upper chamber 16. A lipid (i.e., liquid oils) separation system 61 is also located in the upper chamber 16. The lipid separator 61 includes a partition 60 having an opening 60a, a dam 64 and moat 62 that are formed around the drain valve 18 and cooperate to block lipids from flowing through the drain valve 18 and entering the lower chamber 14. Thus, the shed blood that drains into the lower chamber 14 is substantially free of particles and lipids.
The drain valve 18 located between the two chambers 14, 16 is a conventional, vacuum-operated, duckbill-type drain valve. That is, drain valve 18 includes a pair of opposing lips 80a, 80b that are formed from a flexible or elastomeric material. The two lips 80a, 80b are normally sealed at their outer ends 82a, 82b but may be opened to define an aperture. That is, the ends 82a, 82b of the two opposing lips 80a, 80b are normally in contact with each other, thereby blocking the flow of fluid between the two chambers 14, 16. When a sufficient volume of filtered, lipid-reduced blood builds-up within the drain valve 18, the corresponding fluid pressure exerted on the inside of the flexible lips 80a, 80b causes them to open and allow the blood to flow through the aperture defined thereby and enter the lower chamber 14.
When the lower chamber 14 is full of blood or contains a sufficient volume for reinfusion, the selector valve 38 is moved to the second position, thereby venting the lower chamber 14 to atmospheric pressure. The upper chamber 16 nonetheless remains at vacuum pressure. The pressure differential between the two chambers 14, 16 causes the two lips 80a, 80b of the drain valve 18 to close together, stopping the flow of blood between the two chambers 14, 16, and also preventing vacuum loss in upper chamber 14. The blood in the lower chamber 16 may then be drained to a blood bag 76 for subsequent transfusion. Once the lower chamber 16 has been emptied, the blood bag 76 is sealed-off by a clamp 74 and the selector valve 38 is returned to the first position, allowing filtered, lipid-reduced blood to drain into the lower chamber 14, as described above.
As shown, the '893 system allows processed, recovered blood to be transferred to a blood bag without interrupting the suction being applied to the surgical site. Thus, the '893 system efficiently salvages shed blood without disrupting the drainage of surgical sites. It has been discovered, however, that the duckbill-type drain valve has several disadvantages. First, as described above, the valve is normally in a closed position. That is, the two opposing lips are normally in contact at their outer ends and are only opened in response to fluid pressure exerted by a volume of blood inside the valve. The valve, moreover, is formed from bio-compatible silicone whose physical properties, unlike certain metals and hard plastics, can vary greatly, even if the silicone is manufactured by the same supplier under generally the same conditions. Accordingly, the fluid pressure required to "crack" or break open the prior art valve can vary significantly from one valve to the next. In some instances, the crack pressure may actually exceed the fluid pressure that can practically be generated within the blood recovery system (e.g., the column of blood necessary to open the valve exceeds the height of the upper chamber). This lack of predictability in the crack pressure of the prior art valve raises significant quality assurance issues.
Additionally, sterilization of the '893 system can result in the valve becoming sealed, effectively preventing it from opening at all. More specifically, during sterilization, the '893 blood recovery system, including the duckbill valve, is typically heated to approximately 60.degree. C. At this temperature, the surface of silicone components often becomes "tacky". If two of these "tacky" surfaces are brought into contact with each other, they can adhere to one another. Since the conventional duckbill valve has two silicone lips that are in contact with each other, sterilization can cause the two surfaces to adhere to each other, significantly increasing the force needed to open the valve. Indeed, the volume of fluid required to open the valve may actually exceed the capabilities of the '893 system. Sterilization can thus render the conventional valve inoperable.
Accordingly, a need has arisen for a new valve assembly that preferably opens at zero fluid pressure (e.g., a zero crack-pressure valve), but provides a relatively high fluid flowrate. It is an object of the present invention to provide a valve assembly having zero crack pressure and a high flowrate. It is a further object of the present invention to provide a valve that does not degrade or become inoperable following sterilization. Another object of the present invention is provide a valve that reliably and predictably opens and closes. A further object of the present invention is to provide a valve that closes in response to slight pressure differentials across the valve.